1. Field of the Invention
The present invention relates to an audio amplifier of a portable terminal. More particularly, the present invention relates to an apparatus and method for setting a modulation frequency within a non-used frequency range in order to reduce ElectroMagnetic Interference (EMI) occurring at frequency modulation in a portable terminal.
2. Description of the Related Art
Portable devices are commonly called portable terminals. In recent years, the portable terminal may provide a voice and video call.
In a case of transmitting a voice signal using the portable terminal, the portable terminal amplifies, by a constant gain, a voice signal input through a microphone. After that, the portable terminal converts the amplified voice signal into a high frequency signal and transmits the high frequency signal to the external. In the related art, the gain for amplifying the voice signal in the portable terminal is fixed.
In a case of amplifying a voice signal as above, ElectroMagnetic Interference (EMI) can occur; however, the occurrence of EMI can be reduced by way of a spread spectrum modulation technology. However, the spread spectrum modulation technology is to reduce a radiated peak of EMI as above, so EMI still occurs in all frequency bands.
Because the occurrence of EMI as described above is a cause of inducing an erroneous operation of the portable terminal, manufacturers are exploring methods for reducing the occurrence of EMI. But, the known solutions to address the problem of EMI are imperfect.
Accordingly, to address the above problem, there is a need for an apparatus and method for preventing EMI in a portable terminal.